pH-metric study on determination of proton- ligand stability constants of some substituted pyrazolines

Proton - ligand stability constant (pK) of 1-H-3 - (2" - hydroxy-3" -nitro -5" -methylphenyl) -5-phenyl -Delta(2) - pyrazonlines (L-1), 1-H-3 (2" -hydroxy -3" -nitro -5" -methylphenyl)-5 - (4'-methoxyphenyl) -Delta(2) - pyrazonline (L-2), 1-H-3 - (2" - hydroxy-3" -nitro -5" -methylphenyl) -5 - (3' nitrophenyl) Delta(2) -pyrazonline and 1-H-3-(2" -Hydroxy-3" -nitro -5" -methylphenyl -5 - (3', 4' -methylenedioxyphenyl) -Delta(2) - pyrazonline (L-4) have been investigated pH- metricaly in 70% dioxane - water mixture as a solvent by Calvin-Bjerrum titration technique at 0.1 M ionic strength and at (27 +/- o.1 degrees C) temperature. The Proton - ligand stability constantrs for above ligands are found to be more than pH = 8.0. This showed dissociation of phenolic - OH group. The data obtained were used to determine the standard deviation (sigma) by using diferent values of (n) over bar A of same ligand except the difference in concentration of alkali NaOH.